The contemporary graphics processing architectures follow the virtual pipeline in which the vertices are transformed via vertex shaders, then the pixels are rasterized from triangles, which are then pixel shaded and written to the frame buffer. However not all the triangles produce pixels, because some of them are culled even before the rasterization phase. Unfortunately, the cull runs tend to starve the pixel and compute pipes.
To solve this issue, a hardware mechanism called Position Only Shading pipe (POSH) uses two geometry pipes, a trimmed version called as POSH pipe and a full version called as replay pipe. The POSH pipe runs ahead and records visibility information of the triangles while the replay pipe uses this information to skip the vertices and shade only the passing vertices. Render targets can be subdivided into some number of tiles and then the POSH pipe can be used to do visibility recording per tile and each tile can be processed one after other in the graphics processor.
In the POSH pipe, all the triangles that must go through clipping may be treated as visible. Triangles that lie partially inside the viewport may be treated as visible for all tiles as the POSH pipe itself will not evaluate the entire clipping operation. If the total number of such triangles are fractional percentage of the entire number of triangles that appear at the input of a graphics processor throughout may not be significantly adversely affected.